This invention relates to copper-base alloys having improved punching properties on press and a process for producing them. More particularly, the invention relates to copper-base alloys having improved punching properties on press that are suitable for use in master plates for consumer products such as information/communication small-pitch connectors, semiconductor leadframes, as well as small switches and relays, and a process for producing such alloys.
As the mounting density of consumer electronics, information/communication equipment and automotive parts has increased, connectors, switches, relays, etc. have become increasingly smaller, requiring the use of thinner sheets and finer wires of copper-base alloy materials in these devices.
The parts mentioned above are often worked by punching on high-speed press in combination with a metal mold. During press working, the material undergoes shear deformation with the metal mold punch and then crack propagation starting from the blade tip causes breaking deformation which causes the material to be punched out in a specified shape. As the press is run for an increasing number of shots, the blade tip of the punch wears progressively; as a result, uneven crack propagation occurs from the blade tip and irregularities develop in the breaking profile, as exemplified by an increased difference between shear zone and breaking zone, massive burrs, and heavy tailings of the material that result from the breaking operation; these phenomena all contribute to failure to maintain the desired product shape.
Conventional efforts to increase the mold life include the use of a punch of better material quality, the use of a press lubricant for higher lubricity and clearance settings suitable for various copper-base alloys. However, none of these approaches have offered a complete solution to the problem.
The present inventors conducted intensive studies with a view to solving the aforementioned problems of the prior art. In the fabrication of small-pitch connectors and semiconductor leadframes by punching on high-speed press in combination with a mold, the recent trend is for thinner and narrower pin terminals, specifically in a thickness range of 0.10-0.25 mm and a width range of 0.10-0.30 mm. This design consideration has raised the need for pin terminals to meet the characteristics requirement that they maintain the balance between strength and bending property while exhibiting improved punching properties on press.
An object, therefore, of the present invention is to provide copper-base alloys that are controlled in material""s crystal orientations to exhibit improved punching properties on press.
Another object of the invention is to provide a process for producing such alloys.
For the purposes of the invention, the strength of a pin terminal can be replaced by the 0.2% yield value of the material of which the pin terminal is made. The bending properties of the pin terminal can be replaced by the value of elongation achieved in a tensile test since it undergoes uniaxial deformation when W/txe2x89xa64 (t is the sheet thickness of the pin terminal in millimeters and W is its width in millimeters).
The present invention has been accomplished on the basis of the finding that copper-base alloys having better punching property on press could be obtained by controlling the diffraction intensities of a copper-base alloy material in particular crystal directions among those which were determined by applying X-ray diffraction to the ND plane (which is the surface of the sheet material and hereunder referred to simply as xe2x80x9cND planexe2x80x9d). Specifically, the copper-base alloy of the invention was produced by a process comprising the steps of cold rolling an ingot of a copper-base alloy containing specified amounts of elements such as Sn and Ni, annealing the cold-rolled ingot, and then cold rolling the annealed ingot at a reduction ratio not lower than a specified value as calculated from the contents of non-copper alloying elements. The term xe2x80x9cX-ray diffraction intensityxe2x80x9d as used herein means the integral intensity of crystal directions of the copper-base alloy material measured by an appropriate method such as X-ray diffraction.
The first object of the invention can be attained by a copper-base alloy having improved punching properties on press that contains a total of 0.01-30 wt % of at least one element selected from the group consisting of Sn, Ni, P, Zn, Si, Fe, Co, Mg, Ti, Cr, Zr and Al, with the balance being Cu and incidental impurities, and which has a surface X-ray diffraction intensity ratio SND of at least 10 [SND=I{220}/I{200}; I{220} is the X-ray diffraction intensity of {220} and I{200} is the X-ray diffraction intensity of {200}].
The first object of the invention can also be attained by a copper-base alloy having improved punching properties on press that contains a total of 0.01-30 wt % of at least one element selected from the group consisting of Sn, Ni, P, Zn, Si, Fe, Co, Mg, Ti, Cr, Zr and Al, with the balance being Cu and incidental impurities, and which has a surface X-ray diffraction intensity ratio SND of at least 10 [SND=(I{220}+I{311})/I{200}; I{220} is the X-ray diffraction intensity of {220}, I{311} is the x-ray diffraction intensity of {311}, and I{200} is the X-ray diffraction intensity of {200}].
The first object of the invention can also be attained by a copper-base alloy having improved punching property on press that contains a total of 0.01-30 wt % of at least one element selected from the group consisting of Sn, Ni, P, Zn, Si, Fe, Co, Mg, Ti, Cr, Zr and Al, with the balance being Cu and incidental impurities, and which has a surface X-ray diffraction intensity ratio SDD of at least 10 [SND=(I{220}+I{111})/I{200}; I{220} is the X-ray diffraction intensity of {220}, I{111} is the X-ray diffraction intensity of {111}, and I{200} is the X-ray diffraction intensity of {200}].
The first object of the invention can also be attained by a copper-base alloy having improved punching property on press that contains a total of 0.01-30 wt % of at least one element selected from the group consisting of Sn, Ni, P, Zn, Si, Fe, Co, Mg, Ti, Cr, Zr and Al, with the balance being Cu and incidental impurities, and which has a surface X-ray diffraction intensity ratio SND of at least 10 [SND=(I{220}+I{111}+I{311})/I{200}; I{220} is the X-ray diffraction intensity of {220}, I{111} is the X-ray diffraction intensity of {111}, I{311} is the X-ray diffraction intensity of {311}, and I{200} is the X-ray diffraction intensity of {200}].
In a preferred embodiment, each of the copper-base alloys defined above may contain 0.3-3.0 wt % of Sn.
The second object of the invention can be attained by a process for producing any one of the copper-base alloys described above, which comprises the steps of performing at least one cycle of cold rolling and subsequent annealing on an ingot of a copper-base alloy containing a total of 0.01-30 wt % of at least one element selected from the group consisting of Sn, Ni, P, Zn, Si, Fe, Co, Mg, Ti, Cr, Zr and Al, with the balance being Cu and incidental impurities, and thereafter cold rolling the annealed alloy at a reduction ratio not lower than a specified value as determined from the content of said at least one element.
The second object of the invention can also be attained by a process for producing any one of the copper-base alloys described above, which comprises the steps of performing at least one cycle of cold rolling and subsequent annealing on an ingot of a copper-base alloy containing a total of 0.01-30 wt % of at least one element selected from the group consisting of Sn, Ni, P, Zn, Si, Fe, Co, Mg, Ti, Cr, Zr and Al, with the balance being Cu and incidental impurities, and thereafter cold rolling the annealed alloy at a reduction ratio Z which satisfies the following relation:
Zxe2x89xa7100xe2x88x9210Xxe2x88x92Yxe2x80x83xe2x80x83(1) 
[where Z is the percent reduction by cold rolling; X is the content in wt % of Sn; Y is the total content in wt % of any elements other than Sn].
The second object of the invention can also be attained by a process for producing any one of the copper-base alloys described above, which comprises the steps of performing at least one cycle of cold rolling and subsequent annealing on an ingot of a copper-base alloy containing a total of 0.01-30 wt % of at least one element selected from the group consisting of Sn, Ni, P, Zn, Si, Fe, Co, Mg, Ti, Cr, Zr and Al, with the balance being Cu and incidental impurities, thereafter cold rolling the annealed alloy at a reduction ratio Z which satisfies the following relation:
Zxe2x89xa7100xe2x88x9210Xxe2x88x92Yxe2x80x83xe2x80x83(1) 
[where Z is the percent reduction by cold rolling; X is the content in wt % of Sn; Y is the total content in wt % of any elements other than Sn], and subsequently cold annealing the rolled alloy at a temperature below the recrystallization temperature.
In a preferred embodiment, said cycle or cycles of cold rolling and subsequent annealing are preceded by performing either homogenizing annealing or hot rolling or both on the ingot.